Regulatory Matters - Narrative (Details) - USD ($) $ in Thousands		3 Months Ended
	Apr. 08, 2026	Mar. 31, 2026	Dec. 31, 2025
Regulatory matters:
Net regulatory Assets		$ 92	$ 9,264
Golden State Water Company and Bear Valley Electric Service Inc.
Regulatory matters:
Net regulatory Assets		100
Regulatory asset		122,500
Regulatory liability		122,400
Regulatory asset not accruing carrying costs		44,700
Regulatory liabilities not accruing carrying costs		$ 118,300
Commercial paper, term		90 days
Golden State Water Company and Bear Valley Electric Service Inc. \| Deferred Income Tax Charge
Regulatory matters:
Regulatory liabilities not accruing carrying costs		$ 66,900
Golden State Water Company and Bear Valley Electric Service Inc. \| Pension Costs and Other Postretirement Benefit Costs
Regulatory matters:
Regulatory liabilities not accruing carrying costs		41,000
Golden State Water Company and Bear Valley Electric Service Inc. \| PFAS Contamination Litigation Proceeds Memorandum Account
Regulatory matters:
Regulatory liabilities not accruing carrying costs		10,400
GSWC
Regulatory matters:
Net regulatory Assets		(41,788)	(36,994)
GSWC \| Tyco \| Subsequent Event
Regulatory matters:
Litigation settlement, amount awarded	$ 2,200
GSWC \| Deferred Income Tax Charge
Regulatory matters:
Net regulatory Assets		(63,152)	(63,223)
GSWC \| Pension Costs and Other Postretirement Benefit Costs
Regulatory matters:
Net regulatory Assets		(43,984)	(43,479)
GSWC \| PFAS Contamination Litigation Proceeds Memorandum Account
Regulatory matters:
Net regulatory Assets		(10,406)	(10,987)
BVES
Regulatory matters:
Net regulatory Assets		41,880	46,258
Flowed-through deferred income taxes, net \| Golden State Water Company and Bear Valley Electric Service Inc.
Regulatory matters:
Regulatory asset not accruing carrying costs		25,800
Flowed-through deferred income taxes, net \| GSWC
Regulatory matters:
Net regulatory Assets		22,286	20,932
Derivative instrument memorandum account (Note 5)
Regulatory matters:
Regulatory asset not accruing carrying costs		15,700
Derivative instrument memorandum account (Note 5) \| BVES
Regulatory matters:
Net regulatory Assets		15,708	15,503
Other Regulatory assets \| Golden State Water Company and Bear Valley Electric Service Inc.
Regulatory matters:
Regulatory asset not accruing carrying costs		3,200
2022/2023 general rate case memorandum accounts (unbilled revenue) \| GSWC
Regulatory matters:
Net regulatory Assets		18,814	22,107
2023/2024 General Rate Case Memorandum accounts ( unbilled revenue) \| BVES
Regulatory matters:
Net regulatory Assets		7,237	8,221
Wildfire mitigation and other fire prevention related costs memorandum accounts \| BVES
Regulatory matters:
Net regulatory Assets		$ 9,877	$ 11,336

AMERICAN STATES WATER CO 10-Q